Memory Alpha summary
This whole series was always going to walk a fine line, both on its own terms and how it would be appreciated in the context of the later franchise. It's exactly what the fans have said about Deep Space Nine, Voyager, and Enterprise, a dicey prospect that could and to date has been the only screen Star Trek to be considered unofficial. "The Magicks and Megas-Tu" is a prime example why.
It's not really a good episode. It's an interesting idea, one that would be more fruitfully explored elsewhere, but in and of itself, I would not recommend you watch it, unless you want to be a completist.
Kirk stumbles upon entities who are responsible for humanity's ideas about the Devil. Yeah, sound familiar? Next Generation basically did exactly the same thing, in more believable context, in "Devil's Due." Which is not to say that the idea of beings existing who actually could fit the profile accidentally creating it is a bad one. But this isn't the best way to do it.
The rest of the episode is likewise translated to better effect elsewhere in the form of Q in the Next Generation episode "Deja Q" and Voyager's "Death Wish." Star Trek has a long history of beings possessing extraordinary power abusing it, and usually it's only Kirk making them realize that they've been naughty. In the prolonged Q experience, a much more nuanced exploration became possible, so that even an episode like "Hide and Q," which took a relatively simplistic approach, could be balanced even by a minor entry like "True Q."
"Magicks" doesn't have anything but association going for it. It a series that thought it could do anything just because it was animated finding out that really wasn't the case. It's not the first or even last such misstep, but thankfully still not completely typical. Every Star Trek has episodes like this. Usually fans will interpret the bad ones as those that take risks. "Magicks" is a risk, but other episodes prove how easily it could have been done better. Which makes "Magicks" exactly what it is. Something that looks like this:
|via the Viewscreen|